This invention relates broadly to rotary injection molding of plastic components and, more particularly, pertains to an apparatus and method for injecting and ejecting plastic components in multi-shot injection molding of multi-colored or multi-material plastic parts.
In conventional two-shot molding, the entire mold or portions of the mold are rotated. When the entire mold rotates, this is commonly referred to as the rotary platen technique. This rotation is achieved by a hydraulic cylinder or electric motor, which provides the means of movement for part transfer. This rotation typically would require 180xc2x0 of rotation with other increments possible for additional shots or functions. This rotation is integrated with the movable platen of the machine and cooperates with a fixed metal mold mounted on the stationary platen.
To produce a two-shot plastic part, first one shot of material is injected into the mold, the mold then opens and the platen rotates the mold 180xc2x0, ejects the runners and the mold closes again. A second shot is then injected around the first shot to create a plastic part with two colors or materials. Simultaneously, the first shot is injected again. When the mold opens this time, both runners will eject along with the completed part. The mold will then rotate and close to repeat the cycle again. The rotary platen technique is frequently used because it permits parallel simultaneous injection of both shots. This results in relatively short cycle times, so that production is optimized.
In carrying out the aforedescribed two-shot cycle, it has been found that ejection of the completed part consumes a disproportionate amount of time. Given the fact that the standard injection molding apparatus runs continuously, the time required for the ejection of the completed part over numerous repeated cycles seriously effects overall production.
Accordingly, it is desirable to shorten the time of a conventional two-shot injection molding cycle by having independent control of injection and/or ejection in each respective portion of the mold. That is, the invention contemplates the injection of first and second shots, which can occur independently or simultaneously from each other without regard to ejection of the finished product. The invention allows simultaneous key injection of materials and the ejection of finished product within the molding cycle.
It is a general object of the present invention to provide an injection mold having a high speed, rotary indexing plate assembly used in manufacturing multi-color or multi-layer products.
It is one object of the present invention to provide a three-position, rotary indexing plate assembly which will permit simultaneous injecting and ejecting of plastic components.
It is also an object of the present invention to provide a multi-shot molding process wherein plastic components are transferred among three processing stations in a continuous manner which will improve production.
It is a further object of the present invention to provide a rotary indexing plate assembly driven by a hydraulic cylinder (but not limited to) and traveling along a circular path in 120xc2x0 increments.
It is another object of this present invention to provide a rotary index plate assembly for enabling independent or simultaneous filling of first and second cavities without regard to ejection of the finished product.
In one aspect of the invention, a multi-shot injection mold has at least a first shot cavity and a second shot cavity for receiving injected plastic material to form a completed plastic part which is ejected. The invention is improved by means of an indexing plate rotatably mounted on the injection mold for injecting the first shot cavity and the second shot cavity prior to ejection of the completed plastic part. The injection mold is provided with at least an initial first shot cavity and a second shot cavity and an ejector station. The indexing plate assembly positions common core pins, each of which is selectively cooperable with the first shot cavity, the second shot cavity and the ejector station. The indexing plate is rotatable in 120xc2x0 increments. The injection mold includes a hydraulic cylinder (but not limited to) for incrementally advancing the indexing plate. The injection mold is also equipped with an extension plate having a pair of guide bars with stops fixed thereon and an ejector plate is slidably mounted on the guide bars. The ejector plate includes an ejector cradle for stripping completed plastic components from the core pins. A limit switch is used to control the travel of the ejector plate. The completed plastic components are preferably in the form of over-molded pen barrels.
In another aspect of the invention, a rotary indexing plate assembly is used in producing multi-shot plastic components. The assembly includes a support plate having a first shot cavity and a second shot cavity fixed thereon for receiving plastic injection material to form a first shot and a second shot part, respectively. An ejector station includes an ejector plate having an ejector cradle slidably mounted relative to a portion of the support plate. An indexing plate is rotatably mounted on the support plate, the indexing plate having a first core retainer, a second core retainer, and a third core retainer, each retainer holding common core pins being selectively alignable with the first shot cavity, the second shot cavity and the ejector station. With this construction, when plastic material fills the first shot cavity and the second shot cavity, completed plastic components can be simultaneously removed via the ejector system. The indexing plate is rotatable incrementally to move the first shot part from the first shot cavity to the second shot cavity, move the second shot part from the second shot cavity to the ejector station and move the core pin from the ejector station to the first shot cavity.
In yet another aspect of the invention, there is contemplated a method for producing a two-shot plastic component. The method includes the steps of providing a fixed injection mold having a support plate equipped with a first shot cavity for holding a first shot component, a second shot cavity for holding a second shot component, and an ejector station for removing a two-shot plastic component; providing an indexing plate rotatably mounted to the support plate and having a first core retainer, a second core retainer, and a third core retainer, each of which is selectively alignable with the first shot cavity, the second shot cavity and the ejector station; injecting plastic material into the first shot cavity and the second shot cavity; rotating the indexing plate to move the first shot part to the second shot cavity, move the second shot part to the ejector station and move the third core retainer to the first shot cavity; and further injecting plastic material into the first shot cavity and the second shot cavity regardless of the removal of the two-shot plastic component from the ejector system.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.